Tool control for thread-cutting machines and method of making same



Feb. 2s, 1.928. A 1,660,824

H. W. TRANTER I TOOL CONTROL FOR THREAD CUTTING MACHINES AND METRO!) OF MAKING SAME Filed Oct. 7, 1926 uwmmn HERBERF w. TRANTER Patented FebQZS, 1928.

HERBERT w. TRANTER, or r 'rERBoito, ONTARIO, ANADA.

Teen CONTROL FOR THREAD-CUTTING nonrnns AND MErnonoE. MAKING SAME.

7 Application filed October 7, 1926 Serial No. 140,202..

The invention relates to improvements in the method and apparatus for making teeth of unusual configuration on worms, screws and other cylindrical mechanical elements of general application, and the invention,

particularly relates to an improvement in the method of forming a tooth on dies of the type used in forming helioal'corrugations in metal tubing.

t will be noted from the apparatus illustratedinthe patents to L. H. Brinkman, Numbers 1,120,267, 1,120,268 and 1,120,269, granted December 8, 1914, that the corrugation forming die constituting the tool in such apparatus for forming corrugations in metal isusually in four section's, is provided with a bore sometimes of cylindrical form ai idpreferably slightly tapered for receiving the metal tubing to be corrugated. The

of the thread or tooth be of greater length considered axially or lengthwise of the (he and also flatter at thelarge end of the bore than at the opposite end. This peculiar form of thread is difiicult to construct with.

the mathematical exactness required of dies designed for the purpose herein outlined.

Attempts have been made to avoid the expense and inaccuracies heretofore charac terizing the forming of such threads on die sections nowin general use. One'such suggestion has been to use separate blades inserted in slots in each of the die sections, as shown in the patent to Lewis No. 1,55%,739,

September 22, 1925 This structure has not proven satisfactory in that the blades are flat while the required thread should be curved to the requisite taper with the result that there is a drag between the edges of the flat blades and the tubing inserted in which s r p n o th bl d edges ha l te s y affected the final corrugated tubing.

The primary object of the present inven tion is to provide asimplified means which can be practiced economically to form a "helical thread or corrugation forming teeth of the typeoutlined, and which thread may be formed integral with the body of the die j or its composite sections easily and with mathematical exactness to any desired-configuration, and in which any number of dies '60 may be reproduced as facsimiles of each other and in which all errors due to the personal equation of the duced to a minlmum. I

ting the work blankon an ordinary lathe or similar screw cutting machine and thus avoid necessity of special machines for forming thevaria-bl'e sizes and types of dies necessary with the different sizes. and configurations required in the finished tubing.

operator are r'e- The invention features amethod of cut-. I

f Broadlyth-i's phase of the invention is atf tained by substituting in the conventional lathe, a special-form'of lead screw-in place of the usual uniformpinchlead screw common'on such machinesfor controlling the axial advance of the tool. I 1

Another o'b'ject'of theinvention is to provide a lead screw as a replaceable element of ascrew cuttingapparatus and which may constitute one of aset of' such lead screws each designed to control the advance'of the thread cutting tool with a definite acceleration relative to succeeding units of time-defined by'the speed of rotary movement of the work in the lathe. i

Still another object of the invention. and

featuring accuracy'in the formation ofthe trough between adjacent turns of the thread or tooth in the finished die is toprovide an r I arrangement of controlling grooves in the lead screw which will insure the proper advance of the cutting tool-relativeto its preceding advance and this provides in a me-y chanical way for'the proper degree ofpro-f gresslve narrowing of the trough from one to'the other end of the finished die.

Various other objects and advantages of the invention will be-in part obvious from an inspection of the accompanying drawings I ,andin part will be more fully set forth in the following particular description of one form of device embodying my invention, and

the invention also consists in certain new and novel features of construction and com bination of claimed. I e In the accompanying drawings,

parts hereinafter set forth and Fig. 1 is a view largely diagrammatic of a conventional form of thread cutting latheprovidedwith a lead screw particularly constit ting the subject matter otthe mechanical features oi this disclosure;

Fig. 2 is an enlarged view in side elevation of the lead screw shown at in Fig. 1;

-Fig. 3 is asimilar view ot'a modified form e1"- lcad screw; r Fig. 4t is a'view partlyin axial'section of a die machined by following the method and operation of the machine herein featured and taken axially of the finished work in the lathe on the line 4's of Fig. 5; and

- Fig. 5, is a transverse sectional view taken on the line 55 of Fig. 4.

In the drawings and referring particularly to Fig. 1 there is shown a conventional form of screw orthread cutting lathe including a bed plate 10, tail stock 11, head stock 12,- carrying a die section holding chuck 13 for carrying the die blank sections 15% of which four are shown in Fig. 5. Slidably mounted on the bed plate is the usual compound slide post 15 carrying an L-shaped internal groove cutting tool 16. The post is 'mounted on ;a slide bar 17 and which bar is advanced in: itsbearing 18 by the engagement of a nut. 19 engaging in slots in a lead screw 20. The lead screw isadvanced in a present time relation to the turning chuck 13 by gearing 21 connecting the lead screw withthe head stock spindle 22. It is understood that the apparatus and parts thus far described are conventional andthe showing of a common form of screw lathe in Fig. 1 has been. selected simply to illustrate one mechanism bysmeanso'f which the invention herein featured maybe practiced without necessity of providing special machines for formingthe desired variable pitch thread on the finisl'ied die, best shownin Flg. ,4.

In place of the usual uniform pitch lead screw commonly found at 20 there is sub- V the thread on thefinished die.

stituted a lead screw 1 in which the groove for receiving the nut 19 is formed with a variable taper and with a variable pitch of the order of the pitch and taper required of 7 One such form oflead screw is shown in Fig. 2 where there is disclosed a groove 23 rectangular and substantially square in axial cross sec- -tion and formed as a helix on the outer cylindrical tace'24 ofthe screw. This helical groove ischaracterized by a uniform reductioni'n pitch from'the right towards the left end of the screw, the last turn 25 being in a plane perpendicular to theaxis of the cylinder, indicated by the line a-?), and which groove lead screw. shown in Figs. 1 and 2 is in operative control of the. axial advance of the cutting tool 16., it will be understood that with the tool disposed to extend into the bore 26 of the die sections assembled'ln' able in practicing the method herein featured that the cutting edge be. somewhat rounded. and of course no wider than the width desired in the final fiat turn 26 of the groove in the finisheddie. I

V l Vhenthe first groove is cut the tool is withdrawn, the operation repeated if necessary until the desired depth of cut or rather approximately the desired depth of out has been formed in the die. It will be appre-- ciated that this operation will form a groove of uniform width or rather length when considered axially while the required groove in the finished article is Widest at the right hand side of the bore as shown at 27 in Fig. d and gradually diminishes in width to the minimum width in the final turn of the groove 26 as shown atthe left of Fig. .45 In- .order to form this type ofgroove it is necessary to progressively cut back into the mate rial between the turns oft-he groove making the greatest depth of cut at the right hand end of the bore as shown in Fig. 4: and din1in ishingtl1e cuttowards the left end of the bore and, at the same time it is required, of course, that the taper of the cut be mainained as initially formed. v

This may be attained in two ways. When 'a single groove lead screw 01. the type shown turns otthe' machined screw the sharp edged I tooth shown at 28, Fig. i.

If the indexing of the work has been madeover relatively small angular turns the trough of thegroove 28 will be substantially smooth but should a greater degree of smoothness be required. a

conventional form of grinding toolmay be substituted for the cutting tool herein illustrated and the operation'repeated as has been described for the actuation of the cutting tool. V

Instead of'depending upon the operator surplus material not required between the turns of the finished thread on the die a to index thework in order to gauge out the I form of multiple groove lead screw 30 such as isshown in-Fi'g. 3 may be substituted in i the lathe for controlling t'hetool advance.

Referring to F 3 itis noted thatthe cylinder 31 of the screw 30'is provided with three grooves 32, 33 and 34, each of w ich hasa progressivelydecreasing pitchas has been described for the single groove screw 23 shown in Fig. 2; Succeeding" turns of ad jacent grooves have gradually reducing pitch I screw shown in Fig. 3 in control of the tool,

the nut 19 is first positioned 'in groove 32 and a correspondingly pitched groove '1s' formed inthe die in the manner heretofore described in connection with the formation of the groove when under control of the single groove screw shown in Fig. 2.

Instead of indexing the work as previous ly described, the operator next inserts the controlling nut 19 into the second groove 33 and the cutting operation is repeated as described for the cut formed when the nut was in the first groove 32. It isunderstood that this second cutting operation will widen the groove as at 27' a maximum amount at the right hand end of the die and gradually reducing in its cutting width towards the left end of the die; the tool finally moving into the flat turn 35 previously cut when the tool was under control of the groove 30. The nut is then positioned in the third groove 34 and the operation repeated. as

previously described, the tool cutting a little wider channel; a maximum amount at the right and a minimum amount at the left of the die. It is understood that the cont-rolling lead screw may be provided with any number of grooves of the type of the grooves 33, 34 and 35, but in actual practice it has been found that three grooves are sufficient to give the desired configuration to the grooves which form the thread in the completed die.

The finished die formed of the die sections and mounted in the chuck as shown in Figs. 4 and 5 is in turn mounted in a machine and metal tubing 36 fed therethrough to form the corrugations 37 following conventional practices in this respect.

By fol owing the'means herein suggested in the machining of dies for corrugating metal tubing, it has been possible to form the variable pitch threads required in such dies with mathematical accuracyand there is formed either a continuous thread in an integral die blank or a continual thread in the sectional die blanks illustrated. In either case the thread can be of the theoretical accuracy required of dies used in forming corrugations in thin metal tubing. The

operation of forming such dies has been re- 'duced to nothing-more than a conventional operation of a screw thread formmg machine and advantage is taken of the accuracies in 1 cutting operations characterizing'the operation of such machines. The forming of the thread, at least in so far as its pitch isconcerned,"is entirely independent of the operator, and, as it is possibleto make the lead screw relatively large comparedto the small size of the completed work, an-extremely high degree of accuracy in the formation of the completed thread may be attained simply by the exercising of reasonable accuracy in the formation of'the groove or grooves in the controlling lead screw. v

peatedly' it follows thata large-number of dies may'be manufactured Wltll' the assur- As the same lead s crewmay 'beused reconstructed and there results a uniformity in t-he'corrugation of all of the tubing produced-by the use of any of the dies. 1

Having thus described my invention, I

claim:

1.'In the art'of forming a helical tooth i on a substantially cylindrical body, the method which consists in causing a 'cutting tool to form a helical groove of decreasing pitch with respect to the longitudinal axis of the cylindrical body thereby to form a helical tooth between adjacent turns of the groove, causing the toolto engage a sideof said tooth at one end thereofand to repeat its cut along a path parallel to the previous 1 path whereby the trough between adjacent turns at one end is formed of greater length than adjacent the other end axially of the cylinder and with the trough decreasingin axial length from one to the other end.

2. In the art of forming on a cylindrical, body, a helical tooth with a progressively de creasing length of trough between succeed ing turns of the tooth, the method which'consists in rotating a blank element about its axis, causing a tooth groove forming tool to advance axially of the cylindrical blank and at a progressively slower rate p'er rotary turn of the blank thereby to form a continu ous helical. groove in blank with a uniformly decreasing pitch and causing said tool to repeat its cutting operation along the same pitch line but ofi'set slightly from its previous path of movement. r

3. In a device of the class described, the

I combination of means for mounting a Work blank for rotary movement about an axis, 1

mechanism for rotating said blank, a tool operatively mounted for linear movement parallel to said axis while in operative ren-. gagement withvthe work blank, and control means operatively connected to both the to tary mechanism and the tool to cause anniform acceleration of said linear movement of the tool during Succeeding units of time defined by the rotary movement of the work blank, and means for indexing the work blank between Succeeding linear movements of the tool. v

4. In a lathe structure, the combination of means for cutting a helical tooth with the trough therebetween of greater length axmeans for mounting the same for rotary movement about its axis, a surface of the body provided with a nut recelv ng groove progressively decreasing in pitch from one towards'the other end of the screw and the groove at one end terminating in a plane perpendicular to the axis of the cylindrical h I I .7 v v I i I 6. A lead screw for controlling the advance of a tool in a lathe or equivalent machine, said screw comprising a cylinder hav ing a plurality of helical grooves in, its surface and each groove adapted to receive a nut advanced by the rotation ofthe screw, said grooves each, having'a progressively de creasing pitch from one towards theother end of the screw, the pitch distance between adjacent grooves gradually reducing in length axially'of the screw from one towards the other endand all of said grooves merging into each other at said other end.

7. A lead screw for use in controlling a tool advance in a lathe or similar machine,

said screw providedwith apluralityof nut receiving helical grooves each having a variable pitch, said grooves belng spaced apart at one partiof the screw and merging into a common groove at another part of the SCIGW. V

Signed at New York, in the county of New York and State of New York, this 2nd day of Oct. A. D. 1926.

HERBERT W. TRANTER. 

